From: andrew@...
Date: 2014-07-07T17:09:56+00:00
Subject: [ruby-core:63585] [ruby-trunk - Bug #10013] [CSV] Yielding all	elements from a row

Issue #10013 has been updated by Andrew Vit.


Do you mean that it should consider the block arity to decide whether to yield a Row or destructure it into column parts? i.e.

~~~
CSV.foreach('file.csv', headers: true) do |col1, col2, col3| 
  col1 == "1"
  col2 == "2"
  col3 == "3"
end
~~~
and also
~~~
CSV.foreach('file.csv', headers: true) do |row| 
  row["col1"] == "1"
  row["col2"] == "2"
  row["col3"] == "3"
end
~~~

I think this would be too confusing and magical. What to do when the block arity doesn't match the count of row items? What about the case of a CSV with one column?

I haven't tried, but this might do what you expect (if you must use headers in the input):

~~~
CSV.foreach('file.csv', headers: true).lazy.map(&:to_a).each do |col1, col2, col3| 
  col1 == "1"
  col2 == "2"
  col3 == "3"
end
~~~

I'll leave it for someone else to chime in whether there's a case for a special method here (e.g. "foreach_array").

----------------------------------------
Bug #10013: [CSV] Yielding all elements from a row
https://bugs.ruby-lang.org/issues/10013#change-47638

* Author: Dawid Janczak
* Status: Open
* Priority: Normal
* Assignee: 
* Category: 
* Target version: 
* ruby -v: ruby 2.2.0dev (2014-07-06 trunk 46722) [x86_64-linux]
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN
----------------------------------------
Let's say I have the following CSV file:
col1,col2,col3
1,2,3
4,5,6
(...)

I want to iterate over values yielding them to a block. I can do that like this:
`CSV.foreach('file.csv') { |col1, col2, col3| print col2 + " " } # => "col2 2 5"`
This works fine, but I would like to skip the headers:
`CSV.foreach('file.csv', headers: true) { |col1, col2, col3| print col2 + " " } # => NoMethodError`

CSV yields rows as arrays if headers option is not specified and destructuring works fine.
When headers option is specified however, CSV::Row objects are yielded instead and destructuring fails.

It would be nice to have both scenarios working in the same manner, but I don't know how to approach this. Calling to_a on yielded row (https://github.com/ruby/ruby/blob/trunk/lib/csv.rb#L1731) worked, but obviously this would break when people actually expect CSV::Row instance. Any ideas?



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